Polypropylene laminates

ABSTRACT

A multi-layer laminate containing a layer of a polypropylene material permanently bonded to an imine primed substrate is disclosed. This laminate contains a layer that is a blend of maleated high molecular weight polypropylene/low density polyethylene and a second layer that is substrate, such as nylon, that is primed with an imine primer such as polyethyleneimine.

This is a divisional application of application Ser. No. 07/815,726filed Dec. 30, 1991 now U.S. Pat No. 5,248,364.

FIELD OF THE INVENTION

The present invention relates to laminates and the process for theirproduction. The laminates have a layer of polypropylene containingmaterial bonded to a substrate such as a non-polar substrate. Moreparticularly, the present invention relates to a method of producinglaminates by extrusion coating a layer, a blend of a maleatedpolypropylene and a low density polyethylene, onto a substrate layerprimed with an imine primer.

BACKGROUND OF THE INVENTION

Multi-layered compositions such as permanently bonded laminates are veryuseful. These multi-layered laminates take advantage of the goodproperties of each of the individual layers of the laminate. Laminateshaving good strength, good solvent resistance, good grease resistanceand low gas permeability are very desirable and could be formed from astrong layer, a layer that is solvent or grease resistant and a layerthat has low gas permeability giving the resulting laminate thedesirable overall properties. These laminates have uses in packagingapplications such as the packaging of grease covered metallic parts.

Many laminates that are made of independent layers that aredestructively bonded together are well known and are generally made ofporous substrates and a bonded polymer coating such as a layer ofpolyethylene bonded to a substrate such as paper. However, laminatesusing a non-porous substrate such as metal foil or nylon do notgenerally form permanent bonded layers that are destructive whenseparated. Thus, these non-porous substrates must be primed with somesort of primer to allow permanent bonding of the polymer to thesubstrate. Polyethylenes are permanently bonded to non-porous substratesif the substrate is primed with a polyethylene imine primer. Whereaspolymers of propylene cannot be bonded to these non-porous substrateswithout the use of a very unique primer, a chlorinated polypropyleneprimer. The polypropylene layer in a laminate adds the advantages ofexcellent grease and solvent-resistance to the laminates, however,producing these polypropylene laminates is expensive due to the cost ofthe chlorinated polypropylene primer. Additionally, chlorine containingmaterials are undesirable due to the tendency of forming hydrochloricacid which is very corrosive.

Thus, it would be very desirable to be able to produce inexpensivelaminates containing a layer of polypropylene without the use of achlorinated polypropylene primer.

SUMMARY OF THE INVENTION

The process of the present invention for producing an inseparably bondedpolypropylene melt extrusion laminate comprises extruding onto an imineprimed substrate a layer of a maleated high molecular weightpolypropylene/low density polyethylene blend.

The present invention further comprises an article of manufacture thatis a destructively bonded melt extrusion laminate comprised of

(1) a first layer of a blend of maleated high

molecular weight polypropylene/low density

polyethylene; and

(2) a second layer of a substrate primed with an imine primer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an extrusion lamination process in which the maleatedhigh molecular weight polypropylene/low density polyethylene blend isextruded between a layer of imine primed substrate and polyolefin film.

FIG. 2 represents the extrusion laminated articles illustrating thebenefit of the present invention in which a maleated high molecularweight polypropylene/ low density polyethylene blend is destructivelybonded to imine primed substrates.

DETAILED DESCRIPTION OF THE INVENTION

Applicants have unexpectedly discovered that maleated high molecularweight polypropylene compositions can be inseparably ordestructively-bonded to non-porous substrates primed with imine primer.Prior to the present invention, laminates containing a layer ofpolypropylene on a non-porous substrate were simply not known withoutthe use of a chlorinated polypropylene primer. The laminated film of thepresent invention has excellent toughness as well as excellent barrierproperties against grease, oil, and corrosion, and can be used invarious applications such as wrap applications for metal parts (machineparts).

The process of the present invention entails extruding under extrusioncoating conditions, a layer that is a blend of maleated high molecularweight polypropylene/low density polyethylene onto a substrate that isprimed with an imine primer.

The substrate can be any number of substrates, porous, and non-porous,but is preferably selected from non-porous non-reactive substrates. Bynon-reactive it is meant that the unprimed substrate generally does notaccept the maleated high molecular weight polypropylene/low densitypolyethylene blend to form a destructive bond, either chemically, bypolar interaction, or mechanically. By non-porous it is meant that asubstrate does not have pores sufficient to significantly increase thebonding of the coating to the unprimed substrate. Although poroussubstrates can be used, non-porous substrates are preferred sinceadhesion to these substrates is most improved by the present invention.The non-porous substrates are preferably selected from polymers ofpolycarbonate, polyesters, nylons, and metallic foils such as aluminumfoil, with nylons and metallic foils being more preferred.

The imine primer used to coat the substrate in the present invention ispreferably a polyethyleneimine primer such as Mica A-131-X manufacturedby Mica Corporation, USA. It is expected that other polyethyleneimineswill function well as primer in this application but Mica A-131-X is themost preferred polyethylene imine primer.

The substrate can be primed with the imine primer by any conventionalmethod of priming such as those methods used for priming substrates withwater-based primers. An example of a suitable method of priming thesubstrate is by spraying.

The substrate is preferably primed well in advance of being subjected tothe extrusion coating or extrusion lamination process. The substrate ispreferably coated with a solution containing the imine primer followedby drying the substrate. This solution is preferably an aqueous solutioncontaining very little volatile organics. This solution preferablycontains between about 3-5 volume % polyethyleneimine and 95-97 volume %water.

An example of the extrusion lamination process of the present inventionis illustrated in FIG. 1. In this extrusion coating process 1 is theextruded blend layer of maleated high molecular weight polypropylene/lowdensity polyethylene blend, 2 is the imine coated non-porous substratesuch as nylon film that is laminated to one side of the maleated highmolecular weight polypropylene/low density polyethylene blend layer, and3 is a third layer of an olefin polymer such as a polypropylene orpolyethylene based polymer film or sheet that is laminated with blendlayer 1 to non-porous substrate 2 resulting in the laminated film 4. Theextrusion die that extrudes the layer of maleated high molecular weightpolypropylene/low density polyethylene blend is at 5. The large chilledroll that cools the laminated film is at 6 whereas 7, 8, and 9 are rollsthat aid in pressing and advancing the film.

The extrusion coating process of the present invention is preferablyconducted at a temperature between 425° F. and 525° F. at a line speedof 200 feet per minute or faster, and at a throughput rate of 5 to 10pounds per hour per inch of die width with 10 pounds per hour per inchbeing most preferred.

Any amount of maleated high molecular weight polypropylene would improvethe grease resistance of a film, and would improve the adhesion comparedto a corresponding amount of non-maleated polypropylene. However, themaleated high molecular weight polypropylene/low density polyethyleneblend preferably contains at least 10 weight % maleated high molecularweight polypropylene more preferably at least 30 weight with at least 50weight % being most preferred. The lower amounts of polypropylene in theblend would impart less of the grease and solvent resistant propertiesto the layer, and the adhesion of these low polypropylene blends is notas dramatically improved by the present invention. Therefore the higheramounts of polypropylene are more preferred.

The maleated high molecular weight polypropylene/low densitypolyethylene blend requires some amount of low density polyethylene tobe able to be extrusion coated and preferably contains at least 5 weight% low density polyethylene and no more than 95 weight % maleated highmolecular weight polypropylene. At least 5% low density polyethyleneimparts adequate extrusion coating capabilities to the blend, however10-20 weight % low density polyethylene provides better extrusioncoating properties. The overall balance of adequate extrusion coatingproperties and grease resistance are at a most preferred concentrationof about 90 weight % maleated high molecular weight polypropylene andabout 10 weight % low density polyethylene.

The maleated high molecular weight polypropylene used in the blend ofthe present invention is generally prepared by taking maleated highmolecular weight polypropylene that has been prepared by a conventionalprocess as illustrated in U.S. Pat. Nos. 3,862,266 and 3,862,265. Themaleated high molecular weight polypropylene of the blend is preferablymaleated to about 0.1-2 weight % maleic anhydride, more preferably about0.2-1 weight % with about 0.5 weight % maleic anhydride being mostpreferred. Although the adhesion of the blend is improved byincorporating any amount of maleic anhydride into the high molecularweight polypropylene, at concentrations less than about 0.1 weight %maleic anhydride, the high molecular weight polypropylene does not havean adequate acid number to render the resulting blend destructivelybondable to imine prime substrates, whereas amounts much over 2 weight %do not provide any substantial increase in bonding. The maleated highmolecular weight polypropylene preferably has an acid number between 1and 8, more preferably between 2 and 6 with an acid number of about 4being most preferred.

The high molecular weight polypropylene can be a homopolymer orcopolymer containing up to 5 weight % of other monomers withoutinterfering with the overall properties of the polypropylene. The highmolecular weight polypropylene preferably has a flow rate between 1 and20 decigrams per minute at 230° C. more preferably between 2 and 10decigrams per minute at 230° C. with flow rates between 2 and 5 beingmost preferred. A flow rate above 20 will produce maleated highmolecular weight polypropylenes with flow rates above 70 which meansthat these maleated high molecular weight polypropylenes are too fluidand do not have a desirable melt strength. Whereas a flow rate below 2will produce maleated high molecular weight polypropylenes with flowrates below 40 which means that the maleated high molecular weightpolypropylenes do not process well. Thus the maleated high molecularweight polypropylene preferably has a flow rate between about 40 and 70decigrams/min at 230° C. preferably between about 50 and 60decigrams/min with a flow rate of about 55 decigrams/min being mostpreferred.

The low density polyethylene used in the blend of the present inventionpreferably has a poly-dispersity index between 3 and 15. Thepoly-dispersity index is the ratio of the weight average molecularweight to the number average molecular weight. This poly-dispersityindex for the low density polyethylene is more preferably between about5 and 10 with about 7 being most preferred. A low density polyethylenewith a poly-disperity index below about 3 exhibits excessive edgeweaving during extrusion coating/lamination, whereas a low densitypolyethylene with a poly-dispersity index above about 15 exhibitsextrudate tear-off during extrusion coating/lamination.

The low density polyethylene also preferably has a melt index betweenabout 1 and 10 decigrams/min at 190° C., more preferably between about 3and 7 decigrams with a melt index of about 3.5 decigram being mostpreferred. A low density polyethylene with a melt index below about 1does not blend well with maleated polypropylenes due to a viscositymismatch, whereas a low density polyethylene with a melt index aboveabout 10 is less preferred since it does not provide sufficient meltstrength needed for this process.

The maleated high molecular weight polypropylene/low densitypolyethylene blend of the present invention can have other conventionaladditives incorporated into the blend by conventional methods. Suitableadditives include, for example, Irganox 1010 antioxidant.

The blend of the present invention can be blended by any conventionalprocess such as tumble blending.

Corrosion inhibitors are presently added to some polyethylenes at about0.5% by weight to be made into film for use in laminations forprotecting metal parts from oxidation and corrosion. Examples ofcorrosion-resistant polyethylene films are marketed by NorthernInstruments Corporation, Lino Lakes, Minn., U.S.A., as "Zerust" Films.Such films can be used in combination with a film of the maleated highmolecular weight polypropylene/low density polyethylene blend of thisinvention to form laminated structures with the two films destructivelybonded together. Corrosion inhibitors at about 0.5% by weight could alsobe added to polypropylene films and laminated with a film of the blendof the present invention to form a destructively bonded laminate of thetwo films. Corrosion inhibitors at about 0.5% by weight can also beadded directly to the maleated high molecular weight polypropylene/lowdensity polyethylene blend of this invention for direct extrusioncoating onto a substrate or for extrusion lamination of a multi-layerstructure.

The destructively bonded melt extrusion laminate produced according tothe present invention comprises:

(1) a first layer of a blend of maleated high molecular weightpolypropylene/low density polyethylene; and

(2) a second layer of a substrate primed with an imine primer.

The article manufactured is preferably a co-extrusion that contains athird layer comprised of an olefin polymer that is coated on said firstlayer, said first layer being between said second layer, and said thirdlayer.

The layer of maleated high molecular weight polypropylene/low densitypolyethylene blend that is extruded in contact with the imine primednon-reactive substrate preferably has a thickness between about 0.2 and30 mils (0,005-0.76 mm) more preferably between about 0.5 and 5 mils(0.0127-0,127 mm) with a thickness of about 1-2 mils (0,025-0.05 mm)being most preferred. About 1-2 mils is most preferred because it offersadequate grease proofness to a laminated structure.

The following examples are meant to illustrate the present invention butare not intended to limit the reasonable scope thereof.

EXAMPLES

The following procedures were used to evaluate the examples:

The bond was manually tested to determine if it was destructive, whichmeans that the layers could not be separated without destroying thelamination.

Example 1

Preparation of Maleated Polypropylene. A crystalline polypropylenemixture containing 49 parts by weight (pbw) Tenite polypropylene 423Sfrom Eastman Chemical Company (ECC), 49 pbw Tenite polypropylene 424Sfrom ECC, 1 pbw peroxide, and 1 pbw maleic anhydride was tumble blendedin a drum and charged into an extruder with the following extruderconditions:

Barrel Temperatures: 190° C.-240° C.

Die Temperature: 240° C.-250° C.

Melt Pressure: 40-100 psi

Extruder Screw Speed: 125 rpm

Feed Rate: 10 pound/hour

Vacuum(vent): 2 mm Hg

Residence time: 80-120 second

The extruded product was pelletized and analyzed to have a melt flowrate of 50 dg per minute at 230° C. and an acid number of 5.0 mg KOH pergram.

Example 2

The maleated polypropylene from Example 1 (89.85 pbw), 10 pbw Tenite1550p polyethylene from ECC having a melt index of 3.5 dg per minute,and 0.15 pbw antioxidant were tumble-blended and fed into a twin-screwextruder and pelletized under the same operating conditions as inExample 1. This extruded product was then extruded between a 0.6 milunprimed nylon film (BCF "Curphane" from Bemis Corporation, U.S.A.) anda 2 mil polyethylene film containing 0.5% wt. Zerust corrosion inhibitoras shown in FIG. 1 and illustrated in Run 1, FIG. 2.

Barrel temperature: 450° F.

Melt Temperature: 465° F.

Line Speed: 200 f/min

Film Thickness: 0.001 in

Substrate: nylon film

No bond was formed between the extruded product and the nylon film,however, a good destructive bond was formed between thepolyethylene/Zerust film and the extruded product.

Example 3

This example was conducted essentially identical to Run 1 in Example 2above except that, prior to being coated with the extruded product, thenylon film was coated with a commercial aqueous polyethyleneimine primer(MICA A-131-X from MICA Corporation) as shown in Run 2, FIG. 2. Gooddestructive bonds were obtained from the extruded product with both theprimed nylon film and polyethylene/Zerust film.

Example 4

The blend from Example 2 was extruded onto a polyethyleneimine primedmetal foil substrate as shown in Run 3, FIG. 3. A good destructive bondwas formed between the extruded product and the primed foil.

Example 5

This example was conducted according to Example 4 except that a maleatedpolypropylene was not included in the extruded blend. The extruded blend(Tenite 4G7DP) contained 80 wt. % Tenite 427S polypropylene and 20 wt.Tenite 1550p polyethylene and is illustrated in Run 4, FIG. 2. Nodestructive bond was formed between the extruded layer of thenonmaleated polypropylene/low density polyethylene blend and the foileven with the presence of the polyethylene imine primer on the foilsubstrate.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A destructively bonded extrusion laminate comprising:(1) afirst layer of a blend of maleated high molecular weightpolypropylene/low density polyethylene; and (2) a second layer of asubstrate primed with a polyethyleneimine primer.
 2. The article ofmanufacture according to claim 1 wherein said first layer is about 0.2and 30 mils.
 3. The article of manufacture according to claim 2 whereina third layer comprised of an olefin polymer is coated on said firstlayer, said first layer being between said second layer and said thirdlayer.
 4. The article of manufacture according to claim 3 wherein saidolefin polymer of said third layer contains a corrosion inhibitor. 5.The article of manufacture according to claim 1 wherein said blend ofsaid first layer contains a corrosion inhibitor.
 6. The article ofmanufacture according to claim 1 wherein said substrate of said secondlayer is a non-porous substrate primed with a polyethyleneimine primer.7. The article of manufacture according to claim 1 wherein said blend ofsaid first layer contains at least 30 weight percent maleated highmolecular weight polypropylene.
 8. The article of manufacture accordingto claim 7 wherein said blend contains about 50 to 95 weight percentmaleated high molecular weight polypropylene and about 5 to 50 weightpercent low density polyethylene.
 9. The article of manufactureaccording to claim 1 wherein said maleated high molecular weightpolypropylene of said blend has been maleated with about 0.1 to 2 weightpercent maleic anhydride.
 10. The article of manufacture according toclaim 1 wherein said maleated high molecular weight polypropylene ofsaid blend in said first layer has a melt flow rate of about 40 to 70decigrams per minute at 230° C.
 11. The article of manufacture accordingto claim 1 wherein said low density polyethylene of said blend in saidfirst layer has a polydispersity index between 3 and
 15. 12. The articleof manufacture according to claim 1 wherein said low densitypolyethylene of said blend of said first layer has a melt index betweenabout 1 and 10 decigrams per minute at 190° C.